1. Field of the Invention
The present invention relates to a power supply device for supplying electrical power to a server and the like.
2. Description of the Related Art
In recent years, the scale of data centers is being expanded with the sophistication of Internet services, the use of cloud computing systems, and the like. The number of database servers and the like that are installed at data, centers is increasing, and there is a strong need for increasing the efficiency of power supply devices that supply electrical power to these servers and the like. A loss in a power supply device is converted into Joule heat, thus causing an increase in temperature.
As power supply devices used for computers, power supply devices in which a switching method is used are widely used. In order to increase the efficiency of a power supply device in which a switching method is used, it is effective to design such that the input voltage range of a switching power supply is set be small. In a power supply device 100 shown in FIG. 1 (details are described later), the input voltage range of a transistor used for a second switch S2 through a fifth switch S5 is designed to be small. The winding ratio of a transformer T1 needs to be designed in accordance with the lower-limit voltage in the input voltage range. Thus, when the input voltage range is narrowed, the winding ratio of the transformer T1 can be designed to be large, and the respective duty ratios of the second switch S2 through the fifth switch S5 can be increased for driving. When the respective duty ratios of the second switch S2 through the fifth switch S5 are increased, a peak voltage is lowered, and a loss due to switching is reduced. The cost can be also reduced when a transistor with a small input voltage range is used.
In order to narrow the range of voltages to be input to a first DC-DC converter 40 in the power supply device 100 shown in FIG. 1, a PFC (Power Factor Correction) circuit 30 is provided in a stage preceding the first DC-DC converter 40. It is necessary to turn a first switch S1 on and off when the PFC circuit 30 is being operated, and consuming drive power therefor is thus consumed. In order to reduce this drive power, the PFC circuit 30 is basically stopped when the first DC-DC converter 40 is stopped.
In a power supply device, a switching power supply for generating a control voltage to be used inside and outside the power supply device is mounted in addition to a switching power supply for generating a voltage to be supplied to a load. In the power supply device 100 shown in FIG. 1, a second DC-DC converter 60 corresponds to this switching power supply. There are cases where the second DC-DC converter 60 is operated even when the first DC-DC converter 40 and the PFC circuit 30 are being stopped. In this case, the range of voltages to be input to the second DC-DC converter 60 is not narrowed by the PFC circuit 30. Therefore, it is necessary to design the input voltage range to be relatively large for the second DC-DC converter 60. Under these circumstances, the inventors of the present invention have found a technique for improving the efficiency of a switching power supply for generating a control voltage.